Undecided questions「気付かぬうちに」の「ぬ」

I was listening to a song 'Arigato' by Kokia and came across this sentence in the lyrics 「気付かぬうちに」.I know in Japanese language, some words are omitted and replaced to make it easier to say like for example, 知らない becomes 知らね. Is 気付かぬうちに also the same? But it uses a -u vowel instead of a -e vowel...